[PATCH] Fix generic shift expansion when shift amount is 0

[Keno Fischer]

Yes, see the linked bug report:

  If the shift amount is 0 `shrdl	%cl, %esi, %ebx` acts as `or` (since it's doing shift mod 32), but LLVM seems to assume that it's shifting it out to the left.


http://reviews.llvm.org/D4978

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